1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used as a car transmission or the like.
2. Description of the Related Art
Conventionally, it has been studied to use as a car transmission such a toroidal-type continuously variable transmission as shown in FIGS. 10 and 11. In this toroidal-type continuously variable transmission, an input-side disk 2 is supported concentrically with an input shaft 1 which is rotatably supported in the inside of a transmission case (not shown), while an output-side disk 4 is fixed to the end portion of an output shaft 3 which is also supported rotatable with respect to the transmission case. On the inner surface of the transmission case with the toroidal-type continuously variable transmission stored therein, or on a support bracket disposed within the transmission case, there are disposed two trunnions 5 and 5 which can be respectively swung about their associated pivot shafts respectively situated at positions along an imaginary plane that is perpendicular to an imaginary line connecting the respective axes of the input and output shafts 1 and 3, and distanced from the intersection of the imaginary plane and imaginary line. This physical relation is hereinafter referred to as xe2x80x9ctorsional relationxe2x80x9d.
The two trunnions 5 and 5 are respectively formed of highly rigid metal material, while the above pivot shafts are respectively disposed on the outer surfaces of the two ends of the rigid metal trunnions 5 and 5 in such a manner that they extend concentrically with each other in the front-and-back direction of FIGS. 10 and 11. Also, in the peripheries of displacement shafts 6 and 6 which are respectively disposed in the central portions of the two trunnions 5 and 5, there are rotatably supported power rollers 7 and 7, respectively. And, these power rollers 7 and 7 are interposed between the input-side and output-side disks 2 and 4. On the respective one-side surfaces of the input-side and output-side disks 2 and 4 in the respective axial directions thereof, there are formed an input-side concave surface 2a and an output-side concave surface 4a each of which has an arc-shaped cross section with a point on its associated pivot shaft as a center thereof. And, the peripheral surfaces 7a and 7a of the power rollers 7 and 7, which are respectively formed in rotation-arc-shaped convex surfaces, are contacted with the input-side concave surface 2a and output-side concave surface 4a, respectively.
Also, between the input shaft 1 and input-side disk 2, there is interposed a pressure device 8 of a loading cam type, while the pressure device 8 pushes the input-side disk 2 toward the output-side disk 4. The pressure device 8 is composed of a cam plate 9 rotatable together with the input shaft 1, and a plurality of (for example, 4 pieces of) rollers 11, 11, xe2x80x94which are rotatably held by a retainer 10. On one side surface (in FIGS. 10 and 11, the right side surface) of the cam plate 9, there is formed a cam surface 12 which is a curved surface extending in the circumferential direction of the cam plate 9; and, at the same time, on the outer surface (in FIGS. 10 and 11, the left side surface) of the input-side disk 2 as well, there is formed a similar cam surface 13. And, the plurality of rollers 11, 11, . . . are freely rotatable about their respective shafts extending radially with respect to the center of the input shaft 1. By the way, the input-side disk 2 is supported in such a manner that it can be slided to a slight degree in the axial direction of the input shaft 1 as well as it can be rotated in the rotation direction of the input shaft 1.
If the cam plate 9 is rotated with the rotation of the input shaft 1 to thereby produce a rotation phase difference with respect to the input-side disk 2, then the plurality of rollers 11, 11, xe2x80x94are caused to run up onto the two cam surfaces 12 and 13, thereby causing the cam plate 9 and input-side disk 2 to move away from each other. Since the cam plate 9 is supported on the input shaft 1 carried on the transmission case by a bearing in such a manner that the cam plate 9 is prevented from moving in the axial direction of the input shaft 1, the input-side disk 2 is pushed toward the power rollers 7 and 7, so that the power rollers 7 and 7 are respectively pushed toward the output-side disk 4. On the other hand, the output-side disk 4 is supported to the transmission case in such a manner that it can be only rotated together with the output shaft 3 but is prevented against movement in the axial direction of the output shaft 3. Therefore, the power rollers 7 and 7 are strongly interposed between the input-side disk 2 and output-side disk 4. This increases the mutual contact pressures between the peripheral surfaces 7a, 7a of the power rollers 7, 7 and the two input-side and output-side concave surfaces 2a, 4a to a sufficient degree, so that the rotation of the input-side disk 2 can be transmitted to the output-side disk 4 through the power rollers 7, 7 with little slippage and thus the output shaft 3 with the output-side disk 4 fixed thereto can be rotated.
In changing the rotation speed ratio between the input shaft 1 and output shaft 3, at first, to decelerate the rotation speed between the input shaft 1 and output shaft 3, as shown in FIG. 10, the trunnions 5 and 5 are respectively swung in a given direction about their respective pivot shafts to incline the displacement shafts 6 and 6 in such a manner that the peripheral surfaces 7a and 7a of the rollers 7 and 7 can be respectively contacted with the portion of the input-side concave surface 2a located near the center portion thereof and the portion of the output-side concave surface 4a located near the outer periphery thereof. On the other hand, to accelerate the rotation speed between the input shaft 1 and output shaft 3, as shown in FIG. 11, the trunnions 5 and 5 are respectively swung in the opposite direction to the above direction to incline the displacement shafts 6 and 6 in such a manner that the peripheral surfaces 7a and 7a of the rollers 7 and 7 can be respectively contacted with the portion of the input-side concave surface 2a located near the outer periphery thereof and the portion of the output-side concave surface 4a located near the center thereof. Also, if the inclination angles of the displacement shafts 6 and 6 are respectively set in the middle of the angles shown in FIGS. 10 and 11, then there can be obtained an intermediate gear ratio between the input shaft 1 and output shaft 3.
The basic structure and operation of the toroidal-type continuously variable transmission are as described above. By the way, when using such toroidal-type continuously variable transmission as a transmission for a car including a large output engine, in order to be able to secure the power that can be transmitted, there is employed a structure in which the input-side disks 2 and output-side disks 4 are disposed by twos. In this toroidal-type continuously variable transmission of a so called double-cavity type, the two input-side disks 2 and two output-side disks 4 are respectively arranged in parallel to each other with respect to the transmission direction of the power. FIG. 12 shows an example of a toroidal-type continuously variable transmission of a double-cavity type which has been proposed for the above object.
In the conventional structure shown in FIG. 12, a torque transmission shaft 15, which is a rotary shaft, is supported inside a housing 14 in such a manner that it can be only rotated. And, the torque transmission shaft 15 can be freely driven or rotated by a drive shaft 16 which is connected to the output shaft of a clutch or the like. Also, on the axial-direction two end portions of the torque transmission shaft 15, there are supported a pair of input-side disks 2 and 2 through ball splines 17 and 17 in such a manner that the input-side concave surfaces 2a and 2a of the two input-side disks 2 and 2 are opposed to each other. Therefore, the input-side disks 2 and 2 are respectively supported on the axial-direction two end portions of the torque transmission shaft 15 in such a manner that they can be freely rotated in synchronization with the torque transmission shaft 15 as well as can be freely shifted in the axial direction of the torque transmission shaft 15. Also, on the respective central portions of the back surfaces (the axial-direction opposite surfaces to the input-side convex surfaces 2a and 2a) of the input-side disks 2 and 2, there are formed recessed portions 18 and 18. And, between the deep-side surfaces of the two recessed portions 18, 18 and a loading nut 19 or a securing stepped portion 20 formed in the outer peripheral surface of the torque transmission shaft 15 that is situated near one end (in FIG. 12, the left end) thereof, there are interposed belleville springs 21a and 21b respectively. The two belleville springs 21a and 21b respectively give preloads which are directed toward output-side disks 4 and 4 (which will be discussed next) to the input-side disks 2 and 2. By the way, the elasticity of the belleville spring 21a disposed on the loading nut 19 side is set sufficiently large to thereby substantially prevent the input-side disk 2 opposed to the loading nut 19 from moving in the axial direction thereof.
On the periphery of the intermediate portion of the torque transmission shaft 15, there are supported a pair of output-side disks 4 and 4 in such a manner that they can be freely rotated with respect to the torque transmission shaft 15 while their respective output-side concave surfaces 4a and 4a are opposed to the above-mentioned input-side concave surfaces 2a and 2a. Also, between the mutually opposed input-side and output-side concave surfaces 2a and 4a, there are respectively interposed a plurality of power rollers 7, 7, xe2x80x94(see FIGS. 10 and 11. However, they cannot be seen in FIG. 12, because they are respectively located on the front and back sides of the present toroidal-type continuously variable transmission) which are rotatably supported to the plurality of trunnions 5, 5, xe2x80x94via the displacement shaft 6, 6, xe2x80x94Further, within the housing 14, there is interposed a partition wall 22 between the pair of output-side disks 4 and 4. And, in the inside portion of a through hole 23 formed in the partition wall 22, there is supported a circular-pipe-shaped sleeve 25 by a pair of rolling bearings 24 and 24 which are respectively angular contact ball bearings. The pair of output-side disks 4 and 4 are respectively spline engaged with the two end portions of the sleeve 25 in such a manner that they can be freely rotated together with the sleeve 25. Also, in the intermediate portion of the sleeve 25 and in the inside portion of the partition wall 22, there is fixedly disposed an output gear 26. On the other hand, inside the housing 14, there is rotatably supported an output shaft 27 in parallel to the torque transmission shaft 15. And, a gear 28 fixed to one end (in FIG. 12, the left end) of the output shaft 27 is meshingly engaged with the output gear 26, whereby the rotational movements of the pair of output-side disks 4 and 4 can be taken out freely. Further, between the drive shaft 16 and one (in FIG. 12, left side) input-side disk 2, there is interposed a pressure device 8 of a loading cam type: that is, with the rotation of the drive shaft 16, one input-side disk 2 can be freely driven or rotated while the pressure device 8 is pressing one input-side disk 2 in the axial direction thereof toward its associated output-side disk 4.
Also, on the outer peripheral surface of one end portion of the torque transmission shaft 15, there is formed a flange portion 29 in such a manner that the flange portion 29 is integrally formed with the torque transmission shaft 15. And, between the flange portion 29 and the portion of the outside surface of the cam plate 9 located near the inner periphery thereof, there is interposed a thrust ball bearing 30 of an angular contact type. The thrust ball bearing 30, when the pressure device 8 is in operation, not only allows the mutual displacement between the cam plate 9 forming the pressure device 8 and the torque transmission shaft 15 in the rotation direction thereof, but also supports a thrust load to be applied to the cam plate 9. In order to form such thrust ball bearing 30, an inner race raceway 31 is directly formed on the inside surface (located near the center portion of the torque transmission shaft 15, that is, in FIG. 12, the right-side surface) of the flange portion 29, and an outer race raceway 32 is directly formed in the portion of the outside surface of the cam plate 9 located near the inner periphery thereof, respectively. And, a plurality of balls 33, 33 are rollingly held between the inner race raceway 31 and outer race raceway 32, thereby forming the thrust ball bearing 30. On the outer peripheral surface of the end-face side half section (the half section located near the end portion of the torque transmission shaft 15, that is, in FIG. 12, the left half section) of the flange portion 29, as shown in FIGS. 13 and 14, there are formed a pair of mutually parallel flat surfaces 34 and 34. These flat surfaces 34 and 34, when fastening the loading nut 19 tightly, secure a tool such as a spanner or the like to thereby prevent the rotation of the torque transmission shaft 15.
Further, in order to form the ball splines 17 and 17 which are used to support the pair of input-side disks 2 and 2 on the portions of the torque transmission shaft 15 located near the both ends thereof, two outer-peripheral-surface side spline grooves 35 and 35 are respectively formed in the portions of the outer periphery surface of the torque transmission shaft 15 located near the both ends thereof, and two inner-peripheral-surface side spline grooves 36 and 36 are respectively formed in the inner peripheral surfaces of the input-side disks 2 and 2. And, between the respective outer-peripheral-surface side spline grooves 35 and inner-peripheral-surface side spline grooves 36, there are interposed a plurality of balls 37, 37, xe2x80x94, thereby forming the respective ball splines 17 and 17. Also, the torque transmission shaft 15 includes, in the central portion thereof, an oil supply passage 38 which is shaped in the form of a hollow pipe. And, as shown in FIGS. 12 and 15, two branch oil supply passages 39 and 39 respectively branch off from the oil supply passage 38 in the diameter direction of the cross section of the torque transmission shaft 15, and the respective downstream ends of the two branch oil supply passages 39 and 39 are opened to the bottom portions of the outer-peripheral-surface side spline grooves 35 and 35. Thus, when the present toroidal-type continuously variable transmission is in operation, lubrication oil (traction oil), which is supplied into the oil supply passage 38 by an oil supply pump (not shown), is discharged from the branch oil supply passages 39 and 39 into the outer-peripheral-surface side spline grooves 35 and 35 to thereby lubricate the respective ball splines 17 and 17.
In the above-structured toroidal-type continuously variable transmission, in conjunction with the rotation of the drive shaft 16, the pair of input-side disks 2 and 2, which are respectively supported on the both end portions of the torque transmission shaft 15 through their associated ball splines 17 and 17, are rotated at the same time. And, the rotational movements of them are transmitted to the pair of output-side disks 4 and 4 at the same time and, further, the thus transmitted rotation is then transmitted from the output-side disks 4 and 4 to the output shaft 27, so that the rotation is finally taken out from the output shaft 27. In this operation, since the transmission of the rotational force is carried out by two mutually parallel systems, there can be freely transmitted a large power (torque).
When the power is transmitted from the drive shaft 16 to the output shaft 27, due to the large thrust load generated by the pressure device 8, the input-side and output-side disks 2 and 4 as well as the power rollers 7, 7 interposed between these disks 2 and 4 (see FIGS. 10 and 11) are elastically deformed, respectively. This elastic deformation is absorbed by the axial displacement of the respective input-side disks 2 and 2 with respect to the torque transmission shaft 15. Since the input-side disks 2 and 2 are respectively supported on the torque transmission shaft 15 in such a manner that they can be freely displaced in the axial direction of the torque transmission shaft 15 by their associated ball splines 17 and 17, the absorption of the elastic deformation can be carried out smoothly. Also, because the displacement shafts 6 and 6 (see FIGS. 10 and 11), which are respectively eccentric shafts, pivotally supporting their associated power rollers 7 and 7 are respectively swung about the circular holes (not shown) respectively formed in their associated trunnions 5 and 5, the power rollers 7 and 7 are also displaced in the axial direction of the torque transmission shaft 15 to thereby absorb the above elastic deformation. By the way, since such absorption of the elastic deformation due to the swinging displacement of the displacement shafts 6 and 6 is conventionally known well and does not relate to the characteristic portion of the present invention, the detailed illustration and description thereof are omitted here.
However, in the conventional toroidal-type continuously variable transmission which is structured and operated in the above-mentioned manner, for the following reasons (1) to (3), it is difficult to secure the durability of the torque transmission shaft 15. That is:
(1) Existence of the pair of flat surfaces 34 and 34 formed in the outer peripheral surface of the end-face side half section of the flange portion 29 makes it difficult to secure the durability of the flange portion 29.
(2) It is difficult to secure the hardness of the portion of the torque transmission shaft 15 adjacent to the external thread portion thereof with which the loading nut 19 is to be threadedly engaged. This raises a possibility that, in the torque transmission shaft 15, there can occur damage such as crack or the like at and from the portion adjacent to the external thread portion.
(3) Since the torque transmission shaft 15 includes the branch oil supply passages 39 and 39 with the downstream ends thereof respectively opened to the bottom portions of the outer-peripheral-surface side spline grooves 35 and 35 of the torque transmission shaft 15, these portions are lowered in the torsional rigidity thereof. Due to the lowered torsional rigidity, there arises a possibility that there can be caused damage such as crack or the like at and from the portions of the branch oil supply passages 39 and 39 of the torque transmission shaft 15.
Now, description will be given below in detail of the respective reasons (1) to (3).
Reason (1)
The flat surfaces 34 and 34, as described above, when fastening the loading nut 19 tightly, are used to secure a tool such as a spanner or the like to thereby prevent the rotation of the torque transmission shaft 15. However, actually, the fastening torque of the loading nut 19 is large, that is, equal to or more than 20 kgfxc2x7m. For this reason, the sufficient length L34 (FIG. 13) and width W34 (FIG. 14) of the flat surfaces 34 and 34 must be secured in order to be able to obtain wide engaging areas between the flat surfaces 34 and tool.
On the other hand, on the inner surface of the flange portion 29 where the flat surfaces 34 and 34 are formed, there is formed the inner race raceway 31 which is used to form the thrust ball bearing 30. The contact angle of the thrust ball bearing 30, which is a ball bearing of an angular contact type, as shown by a chained line a in FIG. 14, is inclined toward the center axis of the flange portion 29 as it approaches the outer end face of the flange portion 29. Therefore, if the length L34 and width W34 of the flat surfaces 34 and 34 are set large, then the chained line a passes through the central portions of the flat surfaces 34 and 34 in the longitudinal directions thereof.
In this state, the operation line (which coincides with the chained line xcex1) of the thrust load to be applied to the flange portion 29 through the balls 33, 33 from the cam plate 9 passes through the decreased thickness portion of the flange portion 29 that is caused by the formation of the flat surfaces 34 and 34. In this case, the rigidity of the portion of the flange portion 29 supporting the above thrust load is reduced, which makes it difficult to secure the required durability of the torque transmission shaft 15 including the flange portion 29. If the thickness of the flange portion 29 is increased, then the above operation line is prevented from passing through the decreased thickness portion of the flange portion 29, thereby being able to secure the required durability of the torque transmission shaft 15 including the flange portion 29. However, the increased thickness of the flange portion 29 increases the sizes and weights of the torque transmission shaft 15 and the toroidal-type continuously variable transmission with the present torque transmission shaft 15 incorporated therein. That is, the increased thickness of the flange portion 29 gives rise to an unfavorable problem.
Reason (2)
When forming the external thread portion 40 in the portion of the outer peripheral surface of the torque transmission shaft 15 located near the other end portion thereof for threaded engagement with the loading nut 19, the surface hardness of the external thread portion 40 must be set in such a manner that it is not excessively high. The reason for this is that, if the hardness of the ridge portion of the external thread portion 40 is too high, then there is a fear that there can occur delayed fracture in the external thread portion 40 and, therefore, in order to avoid such delayed fracture, the hardness of the external thread portion 40 must be restrained to the range of HRc20-46. On the other hand, the hardness of the other portions of the surface of the torque transmission shaft 15 than the external thread portion 40 must be set high in order to be able to secure the wear resistance and various strength thereof. For this purpose, after the external thread portion 40 is worked, the surface of the torque transmission shaft 15 is heat-carburized to thereby increase the hardness thereof. And, in the heat carburizing treatment, an anti-carburizing agent is applied to the surface of the external thread portion 40 to thereby prevent the hardness of the external thread portion 40 from becoming excessively high.
Also, on the portion of the torque transmission shaft 15 that is nearer to the central portion thereof than the external thread portion 40, there is formed a stepped surface 41 which extends perpendicularly to the axial direction of the torque transmission shaft 15, in order to bring the inner end face of the loading nut 19 into contact with the stepped surface 41 to thereby position the loading nut 19 in the axial direction of the torque transmission shaft 15. And, the inner peripheral edge of the stepped surface 41 is made to be connected continuously with the end portion of the external thread portion 40 by a curved surface 42 having an arc-shaped section. When the toroidal-type continuously variable transmission is in operation, onto the curved surface 42, there is applied a large tensile stress due to the thrust that is generated by the pressure device 8. In order to prevent the curved surface 42 from being broken in spite of such large tensile stress, it is necessary that the surface hardness of the curved surface 42 is equal to or higher than HRc50.
However, because the curved surface 42 is situated near the end portion of the external thread portion 40, the anti-carburizing agent applied to the external thread portion 40 is easy to stick to the curved surface 42 and, if the anti-carburizing agent sticks to the curved surface 42, then the hardness of the curved surface 42 is lowered down to an insufficient value, which raises a possibility that, in the torque transmission shaft 15, there can occur damage such as crack or the like at and from the curved surface 42 due to the above-mentioned tensile stress.
Also, conventionally, there is known another method in which, prior to working the shape of the external thread portion 40, the torque transmission shaft 15 is heat-carburized to thereby enhance the hardness of the surface of the torque transmission shaft 15; next, the external thread forming portion of the torque transmission shaft 15 is heated again by induction heat treatment and is further annealed to thereby lower the hardness of the external thread forming portion; and, after then, the external thread forming portion is worked into the external thread portion 40.
However, in this conventional method, it is difficult to control the heating area corresponding to the external thread forming portion in the high-frequency heat treatment. That is, there is a fear that even the portion of the torque transmission shaft 15 requiring strength can also be annealed to thereby lower the hardness of such portion.
Reason (3)
A portion of the torque transmission shaft 15, where the outer-peripheral-surface side spline grooves 35 and 35 are formed, receives a large stress in a twisting direction from the balls 37, 37 that respectively form the ball splines 17 and 17. When the branch oil supply passages 39 and 39 are formed in such large stress receiving portion of the torque transmission shaft 15 and thus the cross-sectional area of this portion is reduced by an amount corresponding to the formation of the branch oil supply passages 39 and 39, then the twisting rigidity of this portion is lowered accordingly. Thus, there arises a possibility that, in the torque transmission shaft 15, there can occur damage such as crack or the like at and from the branch oil supply passages 39 and 39 portion thereof. If the diameter of the torque transmission shaft 15 is increased, then the above-mentioned twisting rigidity can be enhanced and thus the required durability of the torque transmission shaft 15 can be secured positively. However, it is not desirable to increase the diameter of the torque transmission shaft 15, because the increased diameter of the torque transmission shaft 15 causes the present torque transmission shaft 15 as well as the toroidal-type continuously variable transmission incorporating the present torque transmission shaft 15 therein to increase in size and weight. This provides another unfavorable problem.
The present invention aims at eliminating all or part of the above-mentioned reasons (1) to (3) found in the conventional toroidal-type continuously variable transmission. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission which can secure the durability of the torque transmission shaft 15 without causing the torque transmission shaft 15 as well as toroidal-type continuously variable transmission to increase in weight and size.
In attaining the above object, according to the invention, there are provided several toroidal-type continuously variable transmissions. Either of them includes: a rotary shaft; at least one input-side disk disposed on the periphery of said rotary shaft in such a manner that it is unrotatable with respect to the rotary shaft but is shiftable in the axial direction of the rotary shaft, the input-side disk including an inside surface having a cross section formed in an arc-shaped concave surface; at least one output-side disk supported on the rotary shaft in such a manner that it is rotatable with respect to the rotary shaft and shiftable in the axial direction of the rotary shaft, the output-side disk including an inside surface having a cross section formed in an arc-shaped concave surface; a flange portion provided in one end portion of the rotary shaft in such a manner it is formed integrally with the rotary shaft; a cam plate rotatable together with the rotary shaft via an angular-type thrust ball bearing disposed in the portion of the rotary shaft located near one end thereof and between the flange portion and the cam plate; a pressure device including the cam plate and interposed between the flange portion and input-side disk for pressing the input-side disk in a direction in which the input-side disk moves away from the cam plate along the axial direction of the rotary shaft; a loading nut threadedly engageable with the portion of the rotary shaft located near the other end portion thereof for restricting mutual shift between the rotary shaft and input-side disk in the axial direction of the rotary shaft; a trunnion swingable about a pivot shaft situated at a torsional relation with respect to the rotary shaft; a plurality of power rollers respectively interposed between the input-side and output-side disks and supported rotatably on a displacement shaft supported by the trunnion, each of the power rollers including a peripheral surface formed in a spherical-shaped convex surface.
Especially, the inner race raceway of the thrust ball bearing is directly formed on the inside surface of the flange portion and, between the inner race raceway and an outer race raceway formed on the cam plate side, there are rollingly held a plurality of balls, whereby the thrust ball bearing is structured. And, the end-face-side half section of the flange portion is formed as a securing portion including an outer peripheral surface of a polygonal cylindrical shape having four or more surfaces, thereby eliminating a possibility that a decreased thickness portion caused by the formation of the securing portion can be present in the direction of the operation line of a load to be applied to the plurality of balls forming the thrust ball bearing.
Also, a external thread portion for threaded engagement with the loading nut is formed on the outer peripheral surface of the rotary shaft located near the other end thereof in the following manner: that is, a cylindrical portion formed in the portion of the rotary shaft located near the other end thereof and having a larger diameter than the outside diameter of the external thread portion is heat-treated together with the remaining portions of the rotary shaft and, next, the surface of the thus treated cylindrical portion is cut off slightly; and, after then, the external thread portion is formed in the thus treated cylindrical portion.
Further, the input-side disk is supported on the outer peripheral surface of the rotary shaft located near the end thereof by a ball spline in such a manner that the input-side disk can be rotated in synchronization with the rotary shaft as well as can be freely shifted in the axial direction of the rotary shaft. Also, the rotary shaft is shaped in the form of a hollow pipe and includes an oil supply passage in the central portion thereof. Further, the downstream side end of a branch oil supply passage, which is used to communicate the oil supply passage with an outer-peripheral-surface side ball spline groove formed on the outer peripheral surface of the rotary shaft, is opened to the bottom portion of the outer-peripheral-surface side ball spline groove. And, the branch oil supply passage is formed in the end portion of the outer-peripheral-surface side ball spline groove at a position thereof that is not opposed to the balls constructing the ball spline.
According to the above-structured toroidal-type continuously variable transmission according to the invention, the durability of the rotary shaft can be enhanced, so that a toroidal-type continuously variable transmission incorporating the present rotary shaft therein can be enhanced in the durability thereof.
At first, the operation line of the thrust load to be applied to the flange portion from the balls of the thrust ball bearing is prevented from passing through the decreased thickness portion of the flange portion, which can make it difficult to cause damage such as crack or the like in the flange portion.
Secondly, the required hardness of the adjacent portion to the external thread portion for threaded engagement with the loading nut can be secured, thereby being able to prevent occurrence of damage such as crack or the like in the adjacent portion. This also makes it possible to lower the hardness of the external thread portion.
Thirdly, a portion of the rotary shaft, where there is formed the outer-peripheral-surface side ball spline groove for constructing the ball spline, is allowed to have a required cross section area, thereby being able not only to enhance the torsional rigidity of the portion but also to prevent stresses from being concentrated on the portion. This makes it possible to prevent occurrence of damage such as crack or the like in the present portion.